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[billbrach]

Hello,

I have a defective controller.  Have used it for 20 years w/o issue.  Zener Diode ZD1 is shorted and I cannot find a schematic that shows its value.

Diode is marked, in 3 areas around the diode, TZX x5C 18 where the x is not legible.  In the past, I've seen many zeners with nothing but their breakdown voltage marked on them.  Elsewhere, I've seen that some X10 controllers run on 18 volts.

Is it safe to assume that my shorted diode is 18 volts ??

Thanks,

Bill Brachhold
Gainesville, FL

[Brian H]

Tried a web search for TZX Series Zener diode.
I found a few vendors with a data sheet available for download.
It may give you the information you need.
Looks speciously like an X10 MC-460 controller. Made for Radio Shack.
Main unit with power supply and switch section diagrams attached.
Has an 18V Zener with a slightly different part number but enough digits match and are in basically the same order.
It is also shown as D1. In the diagram.

[Brian H]

If the unit is that old.
I would also replace the power supply capacitor. For good measure.
I had a Smarthome X10 clone Maxi Controller with an overheating Zener diode.
The filter capacitor was going south and my best guess was the higher than normal ripple currents where overheating it.

[billbrach]

Thanks Brian H, I've already checked both PS caps on my Sencore, and they are fine.  A 1000/25 and a 2.2/450.  I'm betting it's the 18V zener, which I have plenty of. 

Found a used one on eBay for $13, so will take it apart and measure the zener voltage, just to be sure.

And, the schematic you posted doesn't look like a match, as I did not see F1 or T1.  I'll post a picture of the PCB, in the next day or two.

[Brian H]

Sounds like your maybe different.
Photos will help.
I went by the sales photos on Ebay comparing the Radio Shack and the X10 models.
Physically look the same. Maybe different circuity internally or things silk screened differently.

[billbrach]

Just dropping this here for the future.  ZD1 is indeed an 18V/500mw Zener diode.  I didn't have an 18V units, so I series two 9.1V/400mw units and the controller works fine.  Also, the posted schematic, for the X10 MC460 controller appears to be identical, expect the part designators are different.

Thanks for all the help !!

[Brian H]

Glad it helped and you are welcome.
I did a similar thing on a RR501 with a brown warm colored PCB area.
Two 9V Zener diodes in series.